Field of the Invention
The present invention relates to heavy duty pneumatic tires, and in particular to a heavy duty pneumatic tire capable of reducing stone-biting while ensuring drainage performance.
Description of the Related Art
In order to provide drainage performance, a pneumatic tire includes a tread portion provided with at least one main groove with a relatively wide width. In the meantime, when the tire travels on unpaved road around a construction site and the like, the main groove tends to pinch a stone on the road and hold it for a while (it is hereinafter referred to simply as “stone-biting”). The stone-biting tends to occur more easily on heavy duty pneumatic tires having a deep main-groove which is subject to a large ground-contact pressure, and it causes damage on the bottom of the main groove such as crack or chipping.
In order to prevent the stone-biting, Japanese Unexamined Patent Application Publication No. 2008-296795 discloses a tire (t) including a main groove (g) with a bottom (s) provided with a plurality of projections (a) for preventing stone-biting which are spaced in the longitudinal direction of the tire and are separated from both groove walls (h) has been proposed, as illustrated in FIG. 6. These projection (a) can elastically be compressed at the time the main groove (g) has pinched a stone, and then projections (a) can push the stone away from the main groove (g) using the restoring force to reduce stone-biting.
Unfortunately, the projections (a) may deform in contact with the groove walls (h) which narrowed when the main groove comes (g) into contact with the ground, and thus these projections (a) cannot prevent the stone-biting. Furthermore, the projections (a) may bring deterioration of drainage performance of the tire due to reduction of groove volume of the main groove (a).